Hereinafter, a carrier will be briefly described.
A user may carry information in a sine wave or a periodic pulse wave by performing a modulation operation with respect to the amplitude, frequency and/or phase. A sine wave or a pulse wave for carrying information is called a carrier.
Examples of a carrier modulation scheme include a Single-Carrier Modulation (SCM) scheme and a Multi-Carrier Modulation (MCM) scheme. Among others, the SCM scheme involves performing modulation with respect to all information carried on one carrier.
The MCM scheme is a technology of dividing an overall bandwidth channel of one carrier into several sub-channels each having a small bandwidth and transmitting a multiplexed plurality of narrowband sub-carriers through the sub-channels.
In the MCM scheme, each of the sub-channels is approximated to a flat channel due to the limited bandwidth. A user can compensate for channel distortion using a simple equalizer. In addition, the MCM scheme is implemented at a high speed using Fast Fourier Transform (FFT) and is more advantageous in high-speed data transmission than the SCM scheme.
As capabilities of a base station and/or a terminal have been developed, an available frequency bandwidth of the base station and/or the terminal has been expanded. Accordingly, the embodiments of the present invention disclose a multi-carrier system that supports a wideband by aggregating one or more carriers, unlike the MCM scheme.
For example, to increase transmission capacity of wireless data, bandwidths of 200 KHz to 1.25 MHz are used in a 2nd generation wireless communication system and bandwidths of 5 MHz to 10 MHz are used in a 3rd generation wireless communication system. Extended bandwidths of up to 20 MHz are used in a 3GPP LTE system or an IEEE 802.16m system which are 4th generation wireless access systems that have been recently developed.
Although the method of increasing the bandwidth is essential to increase transmission efficiency of wireless data, increasing the bandwidth leads to high power consumption since a high bandwidth should be supported even when low-level services are required. There is also a problem in that the current systems cannot be reused for supporting such requirements.
To overcome such problems, studies have been conducted on a multicarrier transmission method for simultaneously transmitting and receiving a plurality of individual bandwidths.